Stator for a small electric motor



May 3, 1966 E. c. ETTEMA ET AL 3,249,774

STARTER FOR A SMALL ELECTRIC MOTOR Filed June 6, 1962 2 Sheets-Sheet l INVENTORS' EVERHARDUS C.ETTEMA EILDERT KIN GMA Y L A,

AGEN

May 3, 1966 E. c. ETTEMA ETAL STARTER FOR A SMALL ELECTRIC MOTOR 2 Sheets-'Sheet 2 Filed June 6, 1962 Flo FIG.6

INVENTORS EVERHARDUS C. ETTEMA EILDERT KINGMA AUnited States Patent Office 3,249,774 Patented May 3, 1966 STATOR FOR A SMALL ELEC'IRlC MTOR Everhardus Catharinus Ettema and Eildert Kingma, Drachten, Netherlands, assgnors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed June 6, 1962, Ser. No. 206,374 Claims priority, application Netherlands, .lune 23, 1961,

Claims. (Cl. S10- 47) This invention relates to U-shaped cores of magnetic material, the limbs of which are at least substantially at right angles to the connecting piece and coils tightly surrounding this connecting piece.

It is known to build up such coils around formers consisting of a casing-like central piece and two parallel llanges.

According to the invention, the flanges .are made so as tohbe wholly or partly at an angle larger than 0 to each ot er.

This affords the advantage that the winding height on the broad side of the coil is smalle-r than that on the narrow side, resulting in reduced dimensions of the magnetic system. v

It is further known -to build up the coil former of two halves which are slipped around the core, a Winding then being provided thereon which xes the two coilformer halves both with respect to each other and with respect to the core. According to a further aspect of the invention the adjacent faces of the core and/ or the coil former located within the'U and also the opposing external face of the core are shaped so that the coil can be slipped over one of the limbs. This affords the advantage that the coils can be wound separately and then arranged on the core. An additional advantage is that, if the coilbecomes defective, only the coil itself need be replaced and not the core.

A further feature of the invention is that the external face of the core connecting piece is rounded or bevelled at the transition between at least one limb and the connecting piece ofthe U, while the internal face of the core is concave and preferably cylindrical at the transition between at least one limb and the connecting piece of the U.

Another characteristic of the invention is that the external face of the core connecting piece is rounded or bevelled at the transition between at least one limb and the connecting piece of the U, while the face of the coil former located within the U and engaging the connecting piece of the core is protruded and preferably constitutes a cylinder the generatrices of which are at right angles to the axis of the coil former. This affords the advantage that the coil former can be slipped on Ithe core and arranged on the connecting piece veryV rapidly, which is important for mass production.

A further feature of the invention is that, if the U has a symmetrical shape and two coils are arranged on the connecting piece, the concave parts at the transitions between the limbs and the connecting piece are shaped so that an elevation results at -the centre of the connecting piece so that the coils can not be displaced further over the connecting piece. This symmetrical shape has the advantage that in mass production the core is always picked up in the correct position, whereupon the coils can be slipped on it. A further advantage thereof is that the two coils can be held in position by means of one mounting plate.

A further feature of the invention is that the elevation is limited by the concave and preferably cylindrical inner surfaces. An advantage thereof is that the connecting piece can be very short.

A further characteristic of the invention is that the cylindrical faces of the core and of the coils adjoin one another, resulting in the advantage that a maximum crosssect'ion of the core is always obtained.

`lf the core comprises a plurality of stacked metal sheets the sheets need not rst be lxed together, for example by means of rivets, ysince they are enclosed by the walls of the coil former with suflicient tightness.

In order that the invention may be readily carried into effect, it will now be described more fully, by way of example, with reference to the accompanying digrammatic drawing, in which:

FIG. 1 is a plan view of the coil former according to the invention provided with a winding;

FIG. 2 is a side view of the coil,and

FIG. 3 shows a further embodiment of a coil former according to the invention as applied to a stator of an electric machine.

FIG. 4 shows an embodiment of a core in the form of a stator coil for an electric machine of preferably low power, for example a motor for a shaving apparatus;

FIG. Svshows an arrangement for fixing the coil formers of such a core, and FIG. 6 shows further embodiment of such a core.

In FIG. 1, the casing-like central piece of the coil is indicated by 1, While the flanges are indicated by 2 and 3 respectively. From the figure it may clearlyV be seen that the winding height of the winding 4 is considerably smaller on the bottom or broad side 5 than on the upper or narrow'side 6.

When such a coil is used in a stator preferably for an electric machine of 10WA power, for example the electric motor of a shaver, the length l of the motor (FIG. 3) may be reduced by several millimetres, which is very important for such apparatus. The ydimension of the narrow side of the coil is determined by the spacing a between the limbs of the core 7 and that of the broad side by the width b of the U. This structure offers important advantages especially when used in a stator according to FIGS. 4, 5 and 6.

Referring now to FIG. 4, the reference numeral 8 denotes a U-shaped core onto which two coils 9 and 10 can be slipped. The core is provided with convexcylindrical outer faces 11 at the transitions between the limbs and the connecting piece and with concave-cylin-` drical faces 12 on its inner side. The faces 13 of the coil formers co-operating with the said faces have a convex-cylindrical shape and fully adjoin the faces 12 of the core in the mounted condition. The elevation 11 at the centre of the connecting piece prevents slipping of the coils beyond this centre.

As shown in FIG. 5 one side wall of each coil former may be provided with a resilient tongue 15 having a cam 16. If a plate 17of hardpaper is provided with slots 18 so that the distance between the outer sides of the slotsY is somewhat smaller than lthe distance between the outer walls 19 of the coil formers, the said plate can be slipped over the cams 16, as a result of which the tongues 15 are slightly urged towards each other and, upon continued pressing, move apart again when the cams 16 snap behind the hardpaper plate 17, so that the two coil formers and the hardpaper plate on which the terminal wires of the coil may be secured to contacts provided thereon, are rigidly connected together.

FIG. 6 shows a dilferent construction of the core, in which the central elevation of the connecting piece, instead of being constituted by an extension of the concave walls on the inner side of the U, has the form of a cam 20 provided on a dat surface 21 connecting the two concave walls 22.

What is claimed is:

1. A stator for a small electric motor comprising a pair of opposed limb members and a connecting piece both of which define a generally U shaped core, the

inner surfaces of said limb members forming a gap, a hollow coil former concentric with said connecting piece, said coil former having side anges converging toward the gap forming surfaces of said core and a coil on said coil former having a greater depth between the limb members than the depth of said coil adjacent the exterior of the connecting piece of said core; said core and said coil former being shaped so that the coil former can be slipped over a limb of said core and onto the connecting piece of said core.

2. A, stator for a small electric motor according. to claim 1 wherein the exterior surface of the connecting piece of said core is rounded at least at the transition area of the limbs and connecting piece of said core,

and the inner'surface of said connecting piece is concave at least at the said transition area between the limb and connecting piece of said core.

3. A- stator for a small electric motor according to claim 2 wherein the inner surface of said hollow coil former engaging the inner surface of said connecting piece denes an inwardly projecting semi-circle, lthe generatrices of said semi-circle being spaced from and at right angles to the longitudinal axis of said coil former.

4. A stator for a small electric motor according to claim 3 wherein said core is symmetrical and having a pair of inner concave surfaces at each transition area between the limbs of said core, and the connecting piece thereof having a projection defining a elevation therebetween, and a pair of coil formers engaging said concave surfaces and surrounding said connecting piece.

5. An article of manufacture for a low power electric motor comprising the combination of a stator core having opposed limb members and a connecting piece both of which define a generally U-'shaped core, and a coil which slips over a limb of said core onto said connecting piece; said coil comprising a coilv former having means defining a longitudinal through bore, a pair of side iianges converging toward one another at one end thereof and a coil on said coil former having a greatest depth adjacent the converging portions of said anges and a least depth between the dverging portions of said flanges.

References Cited by the Examiner UNITED STATES PATENTS 606,549 6/ 1898 Holmes 310-50 2,945,215 7/1960 Sprude 29-453 3,080,641 3/1963 Marley 29-155.57

FOREIGN PATENTS 784,947 3/ 1935 France.

705,187 3/ 1954 Great Britain.

A 901,164 7/1962 Great Britain.

MILTON O. HIRSHFIELD, Primary Examiner.

ORIS L. RADER, Examiner.

P. L. MCBRIDE, I. I. SWARTZ, Assistant Examiners. 

1. A STATOR FOR A SMALL ELECTRIC MOTOR COMPRISING A PAIR OF OPPOSED LIMB MEMBERS AND A CONNECTING PIECE BOTH OF WHICH DEFINE A GENERALLY U SHAPED CORE, THE INNER SURFACES OF SAID LIMB MEMBERS FORMING A GAP, A HOLLOW COIL FORMER CONCENTRIC WITH SAID CONNECTING PIECE, SAID COIL FORMER HAVING SIDE FLANGES CONVERGING TOWARD THE GAP FORMING SURFACE OF SAID CORE AND A COIL ON SAID COIL FORMER HAVING A GREATER DEPTH BETWEEN THE LIMB MEMBERS THAN THE DEPTH OF SAID COIL ADJACENT THE EXTERIOR OF THE CONNECTING PIECE OF SAID CORE; SAID CORE AND SAID COIL FORMER BEING SHAPED SO THAT THE COIL FORMER CAN BE SLIPPER OVER A LIMB OF SAID CORE AND ONTO THE CONNECTING PIECE OF SAID CORE. 